Heating, ventilating, and air-conditioning (HVAC) systems have been used to ventilate and maintain desirable temperatures within spaces such as buildings, for occupants to live and work, for example. Air conditioning units have been known to reduce the temperature of the air, and various types of heating systems have been used to increase the temperature of the air, including heat pumps, furnaces, electric resistance heat strips, and the like. Many units have been mass-produced and sold, that have provided air conditioning, heating, or both. Systems or units that provide ventilation (i.e., move air) and heat or cool the air (or both) are referred to herein as HVAC systems or units.
Traditional HVAC systems or units used in residential applications cycle on and off. For example, an air conditioning unit (or a unit that both heats and cools that is operating in a cooling mode) may turn on when the temperature in the space reaches a temperature one degree (e.g., Fahrenheit (F) or Celsius or Centigrade (C)) above the thermostat set point temperature, and may turn off when the temperature in the space reaches a temperature one degree below the thermostat set point temperature. Such systems or units keep the temperature within the space close to the set point temperature; however, temperature constantly varies from the top to the bottom of the range or deadband (e.g., from one degree above the temperature set point to one degree below the temperature set point in the above example). In addition, the unit is constantly cycling on and off, and it operates at full capacity and fan speed when it is on. So the occupants of the space are subjected to changes in noise when the unit cycles on and off, and when the unit is on, the noise is at a maximum level. In addition, certain wear occurs at a greater rate due to the cycling on and off of the equipment.
In addition, certain HVAC units have been used that have had variable speed fans or blowers, variable capacity heating or cooling (e.g., variable-speed air conditioning compressors), or both. Some such systems have been used in variable air volume (VAV) systems, for example, and have used variable speed drive units, such as variable frequency AC drive units or variable voltage DC drives. Some such systems have utilized a proportional band control, wherein the capacity of the HVAC system changes as the temperature in the space changes over a range of temperatures and capacitances. The range has been selected in such systems, such that the temperature set point is within the range, at the middle of the range. Further, for example, in an air conditioning mode, the unit may operate at its maximum capacity if the temperature within the space is at or above the top end (maximum temperature) of the temperature range. And the unit may operate at its minimum capacity if the temperature within the space is at or below the bottom end (minimum temperature) of the temperature range.
In such a system, the unit may operate continuously, and the capacity and fan speed changes only when the temperature in the space changes. In addition, except at the maximum end of the temperature range, the unit operates at less than full capacity and less than full blower speed. This reduces the amount of noise under most conditions, and avoids the rapid changes in temperature and noise of units and systems that cycle. Avoiding cycling and operating most of the time at less than maximum capacity has also reduced certain causes of wear.
However, in traditional proportional control systems, under most conditions, the resulting temperature in the space differs from the set point temperature. This is the case unless the capacitance that is needed to maintain a steady temperature also happens to be the capacitance called for at the set point temperature. Consequently, the temperature within the space gradually changes according to the need for heating or cooling, for example, as outside temperatures or solar gain changes. Thus, needs or potential for benefit exist for systems, equipment, and methods that provide for gradual changes in heating or cooling capacity while approaching the set point temperature. Further, needs or potential for benefit exist for such equipment, systems, and methods that are inexpensive, utilize existing components (e.g., to a greater degree than alternatives), are reliable, are easy to place into service by typical installation personnel, or a combination thereof. Needs or potential for benefit exist for such equipment, systems, and methods in typical residential applications, for example, such as mass-produced residential air-conditioning units, heat pumps, furnaces, and the like, that are suitable to be installed by typical installers of such equipment.
In addition, in the prior art, proportional band ranges were usually selected so that the set point was in the middle of the range. However, the typical operating capacity of the system usually differed from this midpoint of the range. Therefore, needs and potential for benefit further exist for systems, apparatuses, and methods wherein the temperature set point is closer to one end of the range than to the other end. Potential for improvement exists in these and other areas that may be apparent to a person of skill in the art having studied this document.